Thank you

Sorry

I'm seeing more reports of an odd font-rendering problem in Firefox: Random lines on a page have fonts with distinct color shifts, pixelating the characters into a "rainbow" that makes the lines nearly illegible. The problem occurs in multiple languages and with many different fonts. All of the reports I've seen can be traced to our favorite problematic Windows automatic update patch, KB 2670838.

Fortunately, it's easy to fix the problem if you disable a specific font rendering in Firefox.

You may recall KB 2670838, the buggy patch Microsoft released down the automatic update chute on Feb. 26. At the time, the primary problem resulted in a Blue Screen of Death on certain Windows 7 machines running specific video driver versions. Microsoft's cleaned up the patch and re-issued it, and if the patch installer detects any of the problematic video drivers, it refuses to install the patch.

There's an official list of 31 incompatible hardware/driver combinations. Most of the incompatible video drivers have new versions available, but a few (including the Lenovo G470/G570/Radeon HD 6370M and 7370M) can't be updated to conform to KB 2670838.

Yesterday a reader approached me with an odd font-rendering problem that only occurs in Firefox. The font shift has been described as pixelated, vertically displaced, with irregularities in smoothing -- a "rainbow" of colors appears where there should be a black font. Oddly, the problem appears on random lines on a Web page and moves when the page is moved up and down the screen. Restarting Firefox doesn't clear up the problem. The same behavior occurs in both Firefox 19 and 20.

The problem also occurs on systems where Internet Explorer 10 has been installed -- even if KB 2670838 was not explicitly installed prior to installing IE10.

To fix the font-rendering problem, you can remove the KB 2670838 patch or uninstall IE10, but uninstalling IE10 and fully restoring IE9 can be complex.

The Mozilla support forum reports that you can usually solve the problem by going into the Firefox about:config page and changing gfx.content.azure.enabled to false. That's kind of a general fix-all approach to many font-rendering difficulties, and in this case it appears to work.

It's not clear if this is a Microsoft issue or a Mozilla issue, but that really muddies the important point: If you have the problem, it's relatively easy to fix. See Mozilla Bug 812695.